Terrible Fuel Mileage - 2000GT

[JstCloseUrEyes]

Hello,

I have a 2000 GP GT with 50K miles on it..

and I am getting terrible gas milage, i'm talking 11.5-12.5 miles per gallon...

Now, the GP is EPA rated at 19 city, so, i figured atleast i should get around 16, but, no

The only mods are a pair of Superturbo mufflers on the back, but would that change the MPG so much?

I had the fuel filter replaced at about 45k miles.

As for my driving, The tac. never goes over 3k rpm really, unless i really have to move, but even then. And i usually do 30-50 on the roads, depending. I do brake hard, but, never slam on them...almost never.

And, every once and a while I think i smell gas under the hood, but, Its never heavy, or constant.

So, is there anything I can do, or am I doomed because i drive like a 19 yearold?

Thanks

[richtazz]

With 50k, you're not really due for a tune-up mileage wise, but time wise you may be. It sounds like either you drive all very short trips or not very often. This type of driving doesn't allow the vehicle to get fully warmed up and burn off carbon and condensation. I would start by having the catalytic converter looked at, as there were problems with GP converters around your model year. A plugged cat will cause horrendous mileage as well as performance issues. I would also change the plugs, wires, pcv, and oxygen sensors, especially if the cat checks out.

[GPFred]

I would also take it out on the highway and run it for a short trip somewhere and then check the mileage. As Richtazz said, there could be carbon buildup and low speed driving over time can build up the carbon. Taking it out on the highway and running it up to speed will cook out that carbon buildup. If you smell gas occassionally from under the hood, you could have a fuel leak somewhere that is not affecting performance but is dropping the mileage thru the floor. Good Luck.

[JstCloseUrEyes]

I was thinking of changing the plugs and wires and the O2's as a matter of fact. I didnt even think of that Cat as being maybe a problem so I will have that checked out.

What brand wires/plugs/O2's do you guys reccomend? Should i stay with all OEM or Delco?

[richtazz]

Stay away from Bosch, especially their multi-electrode junk plugs. I would definitely recommend sticking with OEM/ AC-Delco. Here are the AC-Delco part numbers you need so some parts monkey can't mess you up.

plugs: 41-101 (Iridium)
wires: 746BB
front O-2: AFS109
rear O-2: AFS141
pcv: CV892C

On the PCV valve, be sure to reinstall both o-rings (there's a smaller black one on the PCV itself and a bigger orange one on the housing). Failure to do so can cause the check engine light to come on indicating an EGR insufficient flow due to a vacuum leak that would be created by the missing o-rings.

[JstCloseUrEyes]

Thank you Rich, i appreciate it

but let me ask you a bad question...what is the PCV valve? Im surprised I dont know myself..

[richtazz]

The PCV valve is a weighted check ball for venting crankcase pressure (PCV stands for Positive Crankcase Ventilation). It works off vacuum to draw hydrocarbons and combustion pressure out of the engine. If the PCV valve becomes clogged, it can allow too much pressure to build up in the crankcase causing oil consumption. In the GM 3800 Vin-K (the engine in your car), it's mounting location directly under the MAP (Manifold Absolute Pressure) sensor, can cause other problems due to it causing a vacuum restriction (if clogged) or a vacuum leak (if missing the o-rings and/or retainer spring).